The present invention relates to a photosensitive member which has a photosensitive layer containing a new disazo pigment.
It is known conventionally to use inorganic photoconductive materials such as selenium, cadmium sulfide and zinc oxide as materials constituting photosensitive layers of photosensitive members.
Such photoconductive materials have many advantages, some of which are the capability of being charged to a suitable potential in the dark, the reduced dissipation of the charge in the dark, the fast dissipation of the charge under irradiation of light, and so forth, but, on the other hand, they have various defects. For example, a photosensitive member based on selenium is produced under rigorous manufacturing conditions and at high cost and the product must be handled with care because of susceptibility to heat and mechanical impacts. With respect to the use of cadmium sulfide and zinc oxide for photosensitive members, the products are unable to have long-lasting stability characteristics because the sensitivity cannot be maintained stable in a humid environment and because the colorant added to them as a sensitizer undergoes charge deterioration by corona charging and light fading by exposure to light.
On the other hand, it has also been proposed to use various organic photoconductive polymers including polyvinyl carbazole. These polymers have an advantage over the above-mentioned inorganic photoconductive materials in coating property and lightness, but the polymers are still inferior to the inorganic materials with respect to sensitivity, durability and stability to change of the environment.
In recent years there have been undertaken active researches devoted to the object of eliminating such defects and solving the problems relating to photosensitive members, through which it has been proposed to introduce a photosensitive member of the function-separating type, produced either as a laminate type or as a dispersion type, whose photoconductive function is separated into the charge-generating function and the charge-transporting function and each of these functions is performed by a material differing from that for the other function. Such a photosensitive member of the function-separating type permits the functional materials to be selected from a wide variety of potential materials so that a highly efficient photosensitive member can be obtained by combining most suited functional materials with respect to electrophotographic properties such as charging properties, sensitivity, residual potential, repeating properties, and printing resistance. Such a photosensitive member can be provided at a low cost because the coating method that applies to the production lends itself to a very high productivity. Furthermore, such separation of the functions makes it possible to freely control the photosensitive wavelength range where the charge-generating material has been suitably selected. The charge-generating materials useful for this application are known to be organic pigments dyes which include phthalocyanine pigments, cyanine dyes, polycyclic quinone pigments, perylene pigments, indigo dyes, thioindigo, and methine squarelate dyes.
However, it has been difficult to obtain a photosensitive member of the function-separating type which satisfies the requirements in static properties as a whole. With respect to sensitivity, too, such a photosensitive member has been unsatisfactory and much remains to be improved.